This application relates to the manufacture of a plastic material which has optical qualities suitable for use in mirrors or the like. More specifically, the present invention relates to a process or manufacture of a plastic glass material which is roughly optically equivalent to glass mirrors which are currently in production.
It has long been desirable to utilize plastic materials in vehicle constructions for replacement of glass areas. While glass mirror surfaces are generally adequate for use in vehicle mirrors and the like, the glass mirrored surfaces have several drawbacks. First, the glass is relatively heavy and relatively fragile and, thus, both weight savings and safety considerations would be well served by replacement of standard glass mirrors with a plastic substitute. Secondly, a glass mirrored surface typically does not lend itself to any type of concave or convex bends which may be desirable in certain sophisticated mirror designs.
Therefore, it has been a goal in the art to provide a suitable substitute for glass in mirror construction. In mirrors which have been made with plastic, it has typically been problematic to provide the mirror surface such that the mirror portion transmits through the plastic. The transmissive qualities of most plastics have not been adequate to use in mirror functions, due to various problems with plastic optical properties and aberrations during molding of these materials. Typically, an external mirrored surface does not provide the desired optical quality compared to that of a mirrored glass surface.
Thus, if a mirrored glass surface could be provided using plastics, this would open up various concave, convex or fish-eyed designs or the like, and would provide a lighter vehicle, which is desirable in vehicle construction of today, and would reduce the vibrations inherent in glass mirrors.
In accordance with the present invention, there is provided a process for producing plastic materials suitable for use in a vehicle mirror, comprising first providing an injection mold machine having a cavity therein for forming of a transparent plastic article for simulating glass. The mold includes a pressure sensing and regulating apparatus in the throat of the injection screw. The mold is closed and injected with a clear plastic material. A portion of the mold is thereafter used to pressurize the mold material back into the injection port. Thereafter, the mold is held at a predetermined pressure for optimizing optical properties of the plastic material. This results in a plastic material which has similar optical properties to glass. Thereafter, a mirrored coating is placed on the surface of the plastic material to provide a suitable substitute for a final plastic glass mirror.
A further understanding of the present invention will be had in view of the description of the drawings and detailed description of the invention, when viewed in conjunction with the subjoined claims.